US6885014B2 - Symmetric beamline and methods for generating a mass-analyzed ribbon ion beam - Google Patents

Abstract

Ion implantation systems and beamlines therefor are disclosed, in which a ribbon beam of a relatively large aspect ratio is mass analyzed and collimated to provide a mass analyzed ribbon beam for use in implanting one or more workpieces. The beamline system comprises two similar magnets, where the first magnet mass analyzes the ribbon beam to provide an intermediate mass analyzed ion beam, and the second magnet collimates the intermediate beam to provide a uniform mass analyzed ribbon beam to an end station. The symmetrical system provides equidistant beam trajectories for ions across the elongated beam width so as to mitigate non-linearities in the beam transport through the system, such that the resultant mass analyzed beam is highly uniform.

Description

RELATED APPLICATION

This application is a Continuation-In-Part of Ser. No. 10/136,047 filed May 1, 2002, now U.S. Pat. No. 6,664,547, which is entitled “Ion Source Providing Ribbon Beam with Controllable Density Profile”.

FIELD OF THE INVENTION

The present invention relates generally to ion implantation systems, and more particularly to symmetric beamline systems and methods for generating mass-analyzed ribbon ion beams in an ion implantation system.

BACKGROUND OF THE INVENTION

Ion implantation systems are used to dope semiconductors with impurities in integrated circuit manufacturing. In such systems, an ion source ionizes a desired dopant element, which is extracted from the source in the form of an ion beam of desired energy. The ion beam is then directed at the surface of a semiconductor wafer in order to implant the wafer with the dopant element. The ions of the beam penetrate the surface of the wafer to form a region of desired conductivity, such as in the fabrication of transistor devices in the wafer. The implantation process is typically performed in a high vacuum process chamber which prevents dispersion of the ion beam by collisions with residual gas molecules and which minimizes the risk of contamination of the wafer by airborne particles. A typical ion implanter includes an ion source for generating the ion beam, a beamline system including mass analysis apparatus for mass resolving the ion beam using magnetic fields, and a target chamber containing the semiconductor wafer to be implanted by the ion beam. For high energy implantation systems, an acceleration apparatus is provided between the mass analysis magnet and the target chamber for accelerating the ions to high energies.

In order to achieve a desired implantation for a given application, the dosage and energy of the implanted ions may be varied. The ion dosage controls the concentration of implanted ions for a given semiconductor material. Typically, high current implanters are used for high dose implants, while medium current implanters are used for lower dosage applications. The ion energy is used to control junction depth in semiconductor devices, where the energy levels of the beam ions determine the degree of depth of the implanted ions. The continuing trend toward smaller and smaller semiconductor devices requires a beamline construction which serves to deliver high beam currents at low energies. The high beam current provides the necessary dosage levels, while the low energy permits shallow implants. In addition, the continuing trend toward higher device densities on a semiconductor wafer requires careful control over the uniformity of implantation beams being scanned across the workpiece.

Another continuing trend is toward larger and larger semiconductor wafer sizes, such as 300 mm diameter wafers. Coupled with higher device densities, the larger wafer size increases the cost of individual wafers. As a result, control over implantation uniformity and other parameters is more critical than ever in avoiding or mitigating the cost of scrapping wafers. In many ion implantation systems, a small ion beam (e.g., a pencil beam) is imparted onto a wafer target through mechanical and/or magnetic scanning, in order to provide the desired implantation. The ion beam is shaped according to the ion source extraction opening and subsequent shaping apparatus, such as the mass analyzer apparatus, resolving apertures, quadrupole magnets, and ion accelerators, by which a small ion beam is provided to the target wafer or wafers. The beam and/or the target are translated with respect to one another to effect a scanning of the workpiece. Batch implanters provide for simultaneous implantation of several wafers, which are rotated through an ion beam path in a controlled fashion. Serial implanters, on the other hand, provide implantation of a single wafer at a time.

Where a small ion beam is used, the serial implanters provide a relatively complex target scanning system to impart the beam across the wafer in a uniform manner. For example, mechanical translators are provided to translate the wafer in a single axis, while magnetic apparatus are provided to scan the beam in a perpendicular axis to achieve a raster type scanning of the wafer surface. However, in order to reduce the complexity of such implantation systems, it is desirable to reduce the cost and complexity of target scanning systems, and to provide for elongated ribbon-shaped ion beams. For a ribbon beam of sufficient longitudinal length, a single mechanical scan may be employed to implant an entire wafer, without requiring additional mechanical or magnetic raster-type scanning devices. Such a beam may be employed with serial as well as batch type target scanning systems. However, where a ribbon beam is used in such a single-scan system, it is necessary to ensure that the beam is uniform across the width, in order to provide for uniform implantation of the wafer or wafers. In some prior systems, a small ion beam is mass analyzed, and then collimated to provide a mass analyzed ribbon beam for implanting wafers. Such systems, however, suffer from difficulties in providing a high current beam at low energies due to the high beam density associated therewith, wherein the high beam density tends to result in beam blow-up due to space charge. Accordingly, it is desirable to provide improved ion implantation apparatus and methodologies by which uniform ribbon beams may be provided for implanting semiconductor wafers.

SUMMARY OF THE INVENTION

The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later. The present invention is directed to methods and apparatus for implanting workpieces using an ion beam, by which the above mentioned and other shortcomings associated with the prior art may be overcome or mitigated. In particular, the invention provides implantation systems wherein a relatively wide ribbon-shaped ion beam is produced by an ion source, which is then provided to a symmetric beamline system for mass analysis and collimating. The resulting mass analyzed ion beam has substantially the same transverse width, height, and aspect ratio as the ribbon beam from the source.

The symmetry of the beamline system provides one to one imaging of the source ions of a desired mass onto the target wafer, thereby facilitating control of process parameters such as dose uniformity and implant angular integrity. The invention may be advantageously employed in providing ribbon beams having transverse widths of about 300 mm or more (e.g., 400 mm wide in one implementation) having uniform density profiles, whereby single-scan implantation of large (e.g., 300 mm) wafers can be achieved without complex and costly raster scanning apparatus. Thus, the invention facilitates simplification of implantation systems. In addition, the invention provides a relatively large ion beam cross-section throughout most of the beamline system, whereby the space charge is diffused, which is highly conducive to maintaining beam integrity in low energy implantation applications. Another advantage of the beamline system symmetry is that the total path length or travel distance of ions from the source to the target is nearly constant for all portions of the ribbon beam. Consequently, transport losses are approximately uniform across the beam, and hence do not adversely impact implantation uniformity. Moreover, the architectures of the invention helps in preventing contaminants and particles from the source and beam dumps from reaching the target wafer.

Ion implantation systems and beamline systems therefor are provided, in which a ribbon beam of a relatively large aspect ratio is mass analyzed and collimated to provide a mass analyzed ribbon beam for use in implanting one or more workpieces. The system provides a symmetrical beam path by which the ribbon-beam profile, including aspect ratio, of the initial and analyzed beams are virtually the same. In this regard, the ions traveling through the beamline encounter equidistant trajectories, whereby the travel distance for each ion is the same as that of other ions in the beam. In one example, the beamline system comprises two similar magnets, where the first magnet mass analyzes the ribbon beam to provide an intermediate mass analyzed ion beam, and the second magnet collimates the intermediate beam to provide a uniform mass analyzed ribbon beam to an end station. The symmetrical system provides equidistant beam trajectories for ions across the elongated beam width so as to mitigate non-linearities in the beam transport through the system, such that the resultant mass analyzed beam is highly uniform.

According to one aspect of the invention, an ion implantation system is provided for implanting one or more workpieces with an ion beam. The system comprises an ion source, a beamline system including a mass analyzer, and an end station, which may be a serial or batch implantation station for supporting and/or translating one or more workpieces. The ion source produces an elongated or ribbon-shaped ion beam along a longitudinal beam path having a large aspect ratio of transverse width to height. The mass analyzer receives the elongated ion beam and focuses the beam into a narrow slit that corresponds to a resolving aperture. Ions having differing masses are thus blocked by the aperture, thereby providing ions of only a desired mass.

In one implementation of the invention, the beamline system comprises first and second generally similar magnets, such as electro-magnets, positioned along the beam path, where the first magnet mass analyzes the beam from the ion source, and the second magnet collimates or shapes the resulting intermediate mass analyzed bean to provide a ribbon beam of similar or corresponding width and aspect ratio to input beam, which is then imparted on a workpiece in the end station. The first magnet provides a first magnetic field to the elongated ion beam from the ion source to direct individual ions of a desired mass along the path and to deflect ions of undesired mass away from the path. A resolving aperture may be provided downstream of the first magnet, so as to selectively pass only ions of the desired mass to the second magnet. The second magnet provides a second magnetic field to the ions of the desired mass along the path to direct such ions to the end station as an elongated mass analyzed ion beam comprising an aspect ratio substantially similar to that of the source beam.

The first and second magnetic fields thus operate in symmetrical fashion to guide individual ions of the desired mass to the end station through generally equal distances between the ion source and the end station. The system may further comprise a beamguide defining a beam cavity through which the ion beam travels from an entrance end to an exit end, and quadrupole magnets positioned proximate the resolving aperture to enhance beam confinement and integrity within the beamguide. Multi-cusped magnetic fields may also be provided along at least a portion of the beam path, which may be combined with RF or microwave excitation via a waveguide in the beamguide, so as to create an electron-cyclotron resonance (ECR) condition therein for beam integrity near the resolving aperture.

Another aspect of the invention provides methods for implanting a workpiece using an ion beam in an ion implantation system. The methods comprise creating an elongated ion beam having a first aspect ratio, mass analyzing the elongated ion beam using a first magnetic field, and collimating the ion beam using a second magnetic field to provide an elongated mass analyzed ion beam having a second aspect ratio substantially the same as the first aspect ratio. The methods further comprise providing at least a portion of the elongated mass analyzed ion beam to one or more workpieces for implantation with ions from the elongated mass analyzed ion beam.

To the accomplishment of the foregoing and related ends, the following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed. Other aspects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an ion implantation system in accordance with an aspect of the present invention;

FIG. 2ais a front elevation view illustrating an exemplary ion implantation system in accordance with the present invention;

FIG. 2bis a top plan view further illustrating the ion implantation system ofFIG. 2a;

FIG. 2cis an end elevation view further illustrating the ion implantation system ofFIGS. 2aand2b;

FIG. 3ais a partial perspective view illustrating an exemplary beam path through the beamline system ofFIGS. 2a-2c;

FIG. 3bis a partial side elevation view further illustrating the beam path ofFIG. 3a;

FIG. 3cis a partial top elevation view further illustrating the beam path ofFIGS. 3aand3b;

FIG. 3dis a partial top plan view in section illustrating one magnet and associated magnetic field of the ion implantation system;

FIG. 3eis a partial side elevation view illustrating a portion of the beam path ofFIGS. 3a-3ctogether with quadrupole magnets and a waveguide proximate a resolving aperture in the ion implantation system;

FIG. 4ais a simplified perspective view illustrating a beamguide of the ion implantation system with quadrupoles located proximate the resolving aperture;

FIG. 4bis a simplified perspective view illustrating the beamguide ofFIG. 4awith a waveguide proximate the resolving aperture for beam confinement along the beam path;

FIG. 5ais a bottom plan view illustrating an exemplary ribbon beam source with density profile control apparatus for selectively adjusting a density profile associated with an elongated longitudinal ion beam being in the ion implantation system;

FIG. 5bis a simplified perspective view of the bottom side of the ion source ofFIG. 5aillustrating an elongated ribbon-shaped ion beam extracted therefrom; and

FIG. 6 is a schematic diagram illustrating a beam profile detector and profile control apparatus in the ion implantation system.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described with reference to the drawings wherein like reference numerals are used to refer to like elements throughout. The invention provides methods and systems for provision of a mass analyzed ribbon-beam for ion implantation of workpieces such as semiconductor wafers. One implementation of the invention is illustrated and described hereinafter with respect to the drawing figures. The illustrations and following descriptions are exemplary in nature, and not limiting. Thus, it will be appreciated that variants of the illustrated systems and methods and other such implementations apart from those illustrated herein are deemed as falling within the scope of the present invention and the appended claims.

Referring initially toFIGS. 1, and2a-2c, the invention provides anion implantation system2 comprising anion source4 for producing an elongated (e.g., ribbon-shaped)ion beam6 along a longitudinal beam path. Theion beam source4 includes aplasma source8 with an associated RFexcitation power source9 andextraction apparatus10, which may be of any design by which anelongated beam6 of large aspect ratio is provided. For instance, theplasma source8 may comprise a relatively long plasma confinement chamber from which a ribbon-beam is extracted using a high aspect ratio extraction slit (not shown) in theextraction apparatus10. As illustrated and described in greater detail below with respect toFIGS. 5aand5b, the ribbon-beam6 comprises atransverse width6a(FIG. 2b) and atransverse height6bdefining a first aspect ratio, wherein thetransverse width6ais much larger than thetransverse height6b. It is noted that the dimensions of the ion beams6 and16 illustrated inFIGS. 2aand2bare not necessarily drawn to scale. For example, in the illustratedsystem2, thewidth6aof theelongated ion beam6 extracted from theplasma source8 is more than about 300 mm, such as about 400 mm and theheight6bis a few mm.

Abeamline system12 is provided downstream of theion source4 to receive thebeam6 therefrom, comprising amass analyzer14 positioned along the path to receive thebeam6. Themass analyzer14 operates to provide a magnetic field across the path so as to deflect ions from theion beam6 at varying trajectories according to mass (e.g., charge to mass ratio) in order to provide an elongated mass analyzedion beam16 having a second aspect ratio and profile substantially similar to the first aspect ratio. Thus, as illustrated inFIG. 2b, thewidth16a(e.g., about 400 mm) andheight16bof the mass analyzedribbon beam16 are substantially similar to that of thesource beam6. Anend station18 is provided in thesystem2, which receives the mass analyzedion beam16 from thebeamline system12 and supports one or more workpieces such as semiconductor wafers (not shown) along the path for implantation using the mass analyzedion beam16. Theend station18 includes atarget scanning system20 for translating or scanning one or more target workpieces and theelongated ion beam16 relative to one another. Thetarget scanning system20 may provide for batch or serial implantation.

Thebeamline system12 comprises first andsecond magnets22 and24, respectively, as well as a resolvingaperture26 in a resolvingapparatus31 along the beam path for mass analyzing and collimating functions, in order to produce the elongated mass analyzedribbon beam16. Themagnets22 and24 are supported inbases25, and further components of thebeamline system12 are supported in anenclosure27 with asupport frame29. Thefirst magnet22 comprises first andsecond coils22aand22bproviding a first magnetic field therebetween to theelongated ion beam6 for mass separation of desired mass ions, as illustrated and described further below with respect toFIG. 3d. The ions traveling through the first magnetic field experience a force which directs individual ions of a desired mass along the beam path of thebeamline system12 and which deflects ions of undesired mass away from the path. The resolvingaperture26 passes only those ions of desired mass, while intercepting the undesired ions. Thesecond magnet24 comprises first andsecond coils24aand24b, respectively, located downstream of thefirst magnet22 and the resolvingaperture26 along the path, which provide a second magnetic field to collimate the intermediate mass analyzed ion beam so as to direct individual ions of the desired mass to theend station18 as the elongated mass analyzedion beam16 comprising a second aspect ratio substantially similar to the first aspect ratio.

Themagnets22 and24 in the present example are substantially identical, and provide similar first and second magnetic fields, by which a symmetrical beam path is established through thebeamline system12. In this manner, the first and second magnetic fields guide individual ions of the desired mass across the width of theion beam6 at theion source4 to theend station18 such that the individual ions travel generally equal distances. In this manner, thefirst magnet22 operates as a mass analyzer magnet, and thesecond magnet24 operates as a collimator magnet to provide the mass analyzedribbon beam16 having a uniform density profile and a width of about 400 mm to theend station18. Thesystem2 further comprises abeamguide30 located along the path, which defines a beam cavity through which theion beam6,16 travels from anentrance end32 to anexit end34. Themagnets22 and24 provide the first and second magnetic fields across the path through the beam cavity of thebeamguide30 so as to guide individual ions of a desired mass across the width of theion beam6 at theentrance end32 through thebeam guide30 to theexit end34 such that the individual ions of a desired mass travel generally equal distances therebetween.

Referring now toFIG. 2a, thebeam6 at theentrance end32 of thebeamguide30 arrives from thesource8 as an elongated ribbon, wherein the ions are generally traveling parallel to one another (e.g., in a downward direction inFIG. 2a). Upon encountering the first magnetic field created in thebeamguide30 by themagnet22, the ions of thebeam6 are directed generally to the left in the figure, wherein ions of a desired mass travel through the resolving aperture, and undesired ions are deflected along other trajectories so as to be intercepted by the resolving apparatus or by the side walls of thebeamguide30. By this mass separation, the ion beam downstream of theaperture26 is mass analyzed to include only ions of the desired mass. The second magnetic field from themagnet24 thereafter collimates the mass analyzed beam into aribbon beam16 for use in implanting a workpiece in theend station18.

In order to illustrate the basic beam path, threeexemplary ion trajectories41,42, and43 are illustrated as dashed lines inFIG. 2a, corresponding to the travel paths of three ions of a desired mass, wherein the trajectories41-43 are not necessarily shown to scale. Thefirst trajectory41 comprises first andsecond half trajectories41aand41b, wherein thetrajectory41 begins at an inside end of thebeam6, and ends at an outside end of the mass analyzedribbon beam16. In the first half of thebeamguide30, ions traveling along thetrajectory41aare deflected at anangle51aof less than 90 degrees by operation of the first magnetic field from themagnet22.

Thereafter, thetrajectory41 passes through the resolvingaperture26 at a downward slope, and thesecond half41bof the trajectory begins. Upon encountering the second magnetic field of themagnet24, ions on thetrajectory41bare deflected by asecond angle51bof more than 90 degrees, wherein the sum of theangles51aand51bis 180 degrees by virtue of the symmetry of thebeamline system12, including the substantiallysimilar magnets22 and24 and corresponding first and second magnetic fields. In this manner, ions of appropriate mass traveling along thetrajectory41 are extracted downward from thesource8 at theentrance end32 of thebeamguide30, mass analyzed, and ultimately directed upward at a target wafer in theend station18 at theexit end34.

An exemplary center trajectory42 comprises first andsecond half trajectories42aand42b, wherein ions traveling along the trajectory42 are subjected to equal 90 degree deflections atangles52aand52bby the first and second magnetic fields frommagnets22 and24, respectively. It is noted that the total travel distances along thetrajectories41 and42 are approximately equal. The same is true of the thirdexemplary trajectory43, which comprises first andsecond half trajectories43aand43bbeginning at an outside end of thebeam6 and ending at an inside end of the mass analyzedribbon beam16. In the first half of thebeamguide30, ions traveling along thetrajectory43aare deflected at anangle53aof more than 90 degrees by the first magnetic field and then pass through the resolvingaperture26 at an upward slope. Upon encountering the second magnetic field along thesecond half trajectory43b, ions are deflected upward by asecond angle53bof less than 90 degrees, wherein the sum of theangles53aand53bis 180.

In thesymmetric beamline system12, all ions along the width of the ribbon beam are thus transported along equidistant trajectories, and are each deflected a total of 180 degrees. This symmetric, one to one imaging of the source onto the target wafer advantageously facilitates control of process parameters such as dose uniformity and implant angular integrity, in applications such as single-scan implantation of large (e.g., 300 mm) wafers without complex and costly raster scanning apparatus. In addition, as illustrated further below, the system symmetry provides a relatively large ion beam cross-section throughout most of thebeamline system12. This results in space charge diffusion, which helps to maintain beam integrity in low energy implantation applications. In this regard, although illustrated in the context of the low energyserial implantation system2, the features and aspects of the present invention are also applicable to high and/or medium energy implantation apparatus, such as those employing accelerator stages or modules, as well as to batch implantation systems.

The total path length or travel distance of ions from thesource8 to theend station18 is essentially constant for all portions of theribbon beam6,16. As a result, transport losses are approximately uniform across thebeam16, and hence do not adversely impact implantation uniformity at theend station18. Furthermore, as illustrated and described below with respect toFIGS. 5a,5b, and6, the invention also contemplates the provision of beam profile adjustment apparatus by which beam uniformity at theend station18 can be further facilitated. For example, the density profile of thesource beam6 may be adjusted in order to compensate for transport losses within thebeamline system12, resulting in a uniform density profile of theimplantation beam16.

Moreover, the architecture of thesystem2 aids in preventing contaminants and particles from thesource8 and beam dumps from reaching theend station18. It is noted at this point, that although theexemplary system2, and thebeamline system12 thereof, provide for magnetic deflection of ions through a total of 180 degrees, that other overall deflection angles are contemplated as falling within the scope of the present invention and the appended claims. Thus, the invention specifically contemplates symmetric beamline systems (not shown) in which first and second magnets cooperate to provide either more or less than 180 degree total deflection of ions of a desired mass.

Referring now toFIGS. 3a-3c, theexemplary beam6,16 is further illustrated along the path of thesystem2, including theexemplary trajectories41 and43. Thebeam6 enters thebeamline system12 at theentrance end32 having an elongated ribbon profile of about 400 mm width, and is deflected and mass analyzed by thefirst magnet22, resulting in an intermediate mass analyzedion beam6′, having an aspect ratio different from those of theribbon beam6,16 at theends32,34. Although illustrated inFIGS. 3a-3cas eight exemplary beam trajectories, it is to be appreciated that thebeam6,6′,16 is a continuous distribution of ions traveling along the beam path having a uniform density profile from thesource4 to theend station18. InFIG. 3b, a partial side elevation view of thebeam6,6′,16 is illustrated in a dispersive plane, wherein the various trajectories thereof converge at the center.

Thus, the first magnetic field produced by themagnet22 provides parallel to point type focusing (e.g., for ions of the desired mass) with respect to the center of thebeamline system12 in the dispersive plane to create the intermediate mass analyzedbeam6′. Conversely, the second magnetic field of themagnet24 provides point to parallel type deflection of the ions in the intermediate mass analyzedbeam6′ to provide the elongated mass analyzedion beam16 at theexit end34.FIG. 3cillustrates a top plan view of thebeam6,6′,16 in the non-dispersive plane, where it is seen that ions of the desired mass remain generally in a plane.

FIG. 3dillustrates a partial section view of thefirst magnet22 taken alongline3d—3dofFIG. 3e, including first andsecond coils22aand22b. The illustration inFIG. 3dis typical of the structure of thesecond magnet24 as well, whereby details of thesecond magnet24 are omitted for the sake of brevity. Thecoils22aand22bare located on either side of thebeamguide30, each comprising acylindrical core50 around which conductive coils52 are wound. DC electric current is supplied to thecoils52 via a power source (not shown) in a controlled fashion so as to generate a first dipolemagnetic field54 generally perpendicular to the opposing faces50′ of thecores50. The currents are supplied so as to create magnetic North and South poles at thefaces50′, where a North magnetic pole of thecoil22bfaces a South pole of thecoil22a. Thesecond magnet24 is constructed in similar fashion to provide the second magnetic field in thebeamline system12 for collimating thebeam6′ into an elongated mass analyzedribbon beam16. The first and second magnetic fields can be achieved in a variety of ways, using first and second magnets differing in structure from theexemplary magnets22 and24 illustrated and described herein, and it will be appreciated that all such implementations are contemplated as falling within the scope of the present invention.

Referring also toFIGS. 3eand4a, an initial portion of thebeamline system12 is illustrated inFIG. 3efrom theentrance end32 to the resolvingapparatus31. Thebeamguide30 comprisessections30a,30b, and30cextending from theentrance end32 to the resolvingaperture26, which define the beam path through which beam ions travel. The second half of the beamguide30 (FIG. 4a) comprisescomplimentary sections30c,30b, and30aextending between the resolvingapparatus31 and theexit end34. Where the ions converge in thebeam6′ proximate the resolvingapparatus31, thesystem12 provides beam containment features for maintaining beam integrity. Toward that end, theexemplary beamline system12 comprisesquadrupole magnets60 positioned around thebeamguide sections30con either side of the resolvingaperture26, so as to adjust the location of thebeam waist6′ in the event of space charge effects.

In addition, thebeamguide30 may further comprise a plurality of magnets, such as permanent magnets (not shown) on one or more interior walls of thesections30c, which provide multi-cusped magnetic fields along at least a portion of the path for beam confinement near the resolvingaperture26. Referring also toFIG. 4b, thebeamguide30 may further comprise a waveguide (not shown) within thesections30cproximate the resolvingaperture26 to which an RF or microwave power source (not shown) may be connected via amicrowave feed62. In such an implementation, the microwave power and the multi-cusped magnetic fields interact within thebeamguide30 to provide an electron-cyclotron resonance (ECR) condition for beam confinement along the path within thebeamguide30 near the resolvingaperture26.

Referring now toFIGS. 5aand5b, the invention may be carried out with any appropriateion beam source4 providing anelongated ion beam6 having atransverse width6amuch greater than thetransverse height6b. The illustratedribbon beam source4 comprises aplasma source8 having an elongated outer wall defining a generally cylindricalplasma confinement chamber8′ in which plasma is generated by RF excitation of a source gas using an antenna (not shown) and anRF plasma oscillator9.Extraction apparatus10 provides electric fields via a plurality ofextraction electrodes10ahaving elongated extraction slits orapertures10btherein, where theextraction electrodes10a, theslits10b, and the extractedribbon beam6 are not necessarily drawn to scale. Thesource4 provides thebeam6 having a uniform density profile along thetransverse width6afor provision to theentrance end32 of thebeamguide30 as described above.

In accordance with another aspect of the invention, thesystem2 may also comprisecontrol apparatus70 for selectively adjusting the density profile associated with anelongated ion beam6 being extracted from theribbon beam source4. Thecontrol apparatus70 comprises a plurality of magnet pairs80 proximate the extraction exit opening in theplasma source wall8 through which thebeam6 is extracted. The magnet pairs80 individually comprising upper and lower electro-magnets80aand80bhaving energizable windings through which current may be conducted in a controlled fashion so as to provide adjustablemagnetic fields82 between themagnets80aand80b.

Themagnets80aand80bare disposed on either side of the exit opening to provide adjustablemagnetic fields82 in an extraction region between the exit opening of theplasma source8 and theextraction electrodes10aso as to adjust the density profile of an extractedribbon beam6. The electro-magnets80 are energized such thatfirst magnets80aprovide magnetic poles of a first magnetic polarity (e.g., North in the illustrated example) facing thesecond magnets80b, and thesecond magnets80bprovide magnetic poles of an opposite second magnetic polarity (South) facing thefirst magnets80a. In this fashion, themagnets80aand80bof each magnet pair cooperate to provide the adjustablemagnetic fields82 in the extraction region.

Themagnetic fields82 associated with each pair of magnets80 may be individually adjusted using acontrol system72 providing control signals to DC power supplies74 to energize coil windings associated with the individual electromagnets80. Thecontrol system72 is connected to thepower sources74 to individually control the currents supplied to the magnet pairs so as to individually adjust themagnetic fields82 produced by the magnet pairs80 in the extraction region according to a desired plasma density profile for the extractedion beam6. This control over theindividual fields82 allows selective restriction on the amount of ionized plasma available at the extraction region, wherein increasing themagnetic field82 associated with a given magnet pair reduces the amount of plasma flow out of thechamber8′ proximate that pair. Thus, thetransverse width6aof theribbon beam6 is segmented into eight portions or slices, each being associated with a magnet pair80. The ability to selectively restrict plasma flow out of thechamber8′ for each of the slices allows control over the density profile of theresultant beam6 as it is extracted.

Referring also toFIG. 6, beam density profile control may be done according to a desired profile at thesource4, or according to a desired profile downstream at theend station18 using known control algorithms, including but not limited to feedback, feed-forward, predictive or other types. This provides utility, for example, in correcting or compensating for non-uniformities in thesource4 or in downstream devices in theimplantation system2. Thus, theimplantation system2 may include abeam profile detector90 located at theend station18 to measure the density profile of thebeam16 as it is imparted on a target wafer or wafers, and to provide corresponding measurement signals to thecontrol system72 of thecontrol apparatus70. Thecontrol system72, in turn, may make appropriate adjustments to energize the electro-magnets80 (e.g., using the power supplies74) so as to correct for any deviations from the desired profile at the workpiece. Thebeam profile detector90 may be of any appropriate type, for example, such as a plurality of Faraday cups positioned in theend station18 so as to detect an actual density profile associated with the elongated mass analyzedion beam16.

The exemplaryion implantation system2 illustrated and described above provides for an elongated ribbon beam of uniform density having a generally rectangular transverse profile, which may be advantageously employed with a serialimplantation end station18. In such an application, the resulting mass analyzedribbon beam16 may be scanned across the wafer surface, for example, using a single-scan mechanical translation of the target wafer (not shown). The invention also finds application in association with batch implant typetarget scanning systems20, wherein a plurality of wafers may be angularly translated through the path of the elongated mass analyzedion beam16. In such applications, the extraction slits10bof theextraction apparatus10 may be trapezoidal in shape, in order to accommodate the angular scanning of the wafer surfaces, thereby providing uniformity in the implantation of the wafers. It will be appreciated that many other such modifications may be made to the illustrated apparatus and systems without departing from the scope of the present invention.

Although the invention has been illustrated and described above with respect to a certain aspects and implementations, it will be appreciated that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure, which performs the function in the herein illustrated exemplary implementations of the invention. In this regard, it will also be recognized that the invention includes a computer-readable medium having computer-executable instructions for performing the steps of the various methods of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “includes”, “including”, “has”, “having”, “with” and variants thereof are used in either the detailed description or the claims, these terms are intended to be inclusive in a manner similar to the term “comprising”.

Claims (31)

1. An ion implantation system for implanting one or more workpieces with an ion beam, comprising:

an ion source producing an elongated input ion beam along a longitudinal path, the input ion beam comprising a first transverse width and a first transverse height near the source, the first transverse width and the first transverse height defining a first aspect ratio as a ratio of the first transverse width and the first transverse height, wherein the first transverse width is larger than the first transverse height,

a beamline system comprising a mass analyzer positioned downstream from the ion source along the path to receive the elongated input ion beam at an entrance end of the beamline assembly, the mass analyzer providing a magnetic field across the path so as to deflect ions from the input ion beam at varying trajectories according to mass to provide an elongated mass analyzed ion beam including ions of a desired mass, the mass analyzed ion beam comprising a second transverse width and a second transverse height at an exit end of the beamline assembly, the second transverse width and the second transverse height defining a second aspect ratio as a ratio of the second transverse and the second transverse height; and

an end station proximate the exit end of the beamline assembly, the end station receiving the mass analyzed ion beam from the beamline system and supporting at least one workpiece along the path for implantation using the mass analyzed ion beam;

wherein the second aspect ratio is substantially the same as the first aspect ratio.

2. The ion implantation system ofclaim 1, wherein the beamline system comprises:

a first magnet providing a first magnetic field to the elongated input ion beam from the ion source, the first magnetic field operating to direct individual ions of a desired mass along the path and to deflect ions of undesired mass away from the path; and

a second magnet located downstream of the first magnet along the path, the second magnet providing a second magnetic field to the ions of the desired mass along the path between the first magnet and the end station, the second magnetic field operating to direct individual ions of the desired mass to the end station as the elongated mass analyzed ion beam.

3. The ion implantation system ofclaim 2, wherein the first and second magnets provide the first and second magnetic fields so as to guide individual ions of the desired mass across the width of the ion beam at the ion source to the end station such that the individual ions of the desired mass travel generally equal distances between the ion source and the end station.

4. The ion implantation system ofclaim 3, wherein the first transverse width of the elongated input ion beam is about 400 mm near the ion source, and wherein the second transverse width of the elongated mass analyzed ion beam about 400 mm near the end station.

5. The ion implantation system ofclaim 2, wherein the first magnet comprises a mass analyzer magnet and the second magnet comprises a collimator magnet.

6. The ion implantation system ofclaim 2, wherein the first and second magnets are substantially identical.

7. The ion implantation system ofclaim 1, wherein the first transverse width of the elongated input ion beam is about 400 mm near the ion source, and wherein the second transverse width of the elongated mass analyzed ion beam about 400 mm near the end station.

8. The ion implantation system ofclaim 1, wherein the mass analyzer comprises a beamguide located along the path, the beamguide defining a beam cavity through which the ion beam travels from the entrance end to the exit end, wherein the mass analyzer provides the magnetic field across the path through at least a portion of the beamguide to guide individual ions of a desired mass across the width of the input ion beam at the entrance end through the beam guide to the exit end such that the individual ions of a desired mass travel generally equal distances between the entrance and exit ends of the beamguide.

9. The ion implantation system ofclaim 8, wherein the mass analyzer comprises first and second magnets and the beamguide comprises a resolving aperture between the first and second magnets along the path;

wherein the first magnet is positioned near the entrance end to provide a first magnetic field along the path between the entrance end and the resolving aperture so as to deflect ions from the input ion beam at varying trajectories according to mass, the first magnetic field operating to direct individual ions of a desired mass through the resolving aperture along the path and to deflect ions of undesired mass away from the aperture;

wherein the resolving aperture is positioned downstream of the first magnet along the path and comprises a transverse width and a transverse height defining a resolving aperture aspect ratio different from the first and second aspect ratios; and

wherein the second magnet is positioned near the exit end along the path to receive ions of a desired mass traveling through the resolving aperture, the second magnet providing a second magnetic field along the path between the resolving aperture and the exit end, the second magnetic field operating to direct individual ions of the desired mass from the resolving aperture to the exit end along the path so as to provide the mass analyzed ion beam comprising the second aspect ratio.

10. The ion implantation system ofclaim 9, wherein the first and second magnets provide the first and second magnetic fields so as to guide individual ions of the desired mass across the width of the input ion beam at the ion source to the end station such that the individual ions of the desired mass travel generally equal distances between the ion source and the end station.

11. The ion implantation system ofclaim 9, wherein the first magnet comprises a mass analyzer magnet and the second magnet comprises a collimator magnet.

12. The ion implantation system ofclaim 9, wherein the first and second magnets are substantially identical.

13. The ion implantation system ofclaim 9, wherein the first transverse width of the elongated input ion beam is about 400 mm near the ion source, and wherein the second transverse width of the elongated mass analyzed ion beam is about 400 mm near the end station.

14. The ion implantation system ofclaim 9, wherein the end station further comprises a beam profile detector detecting a density profile associated with the elongated mass analyzed ion beam at the end station, and wherein the ion source further comprises a beam profile control apparatus operable to adjust a density profile associated with the elongated input ion beam near the ion source according to a detected density profile associated with the elongated mass analyzed ion beam at the end station.

15. The ion implantation system ofclaim 14, wherein the beam profile detector comprises a plurality of Faraday cups positioned in the end station so as to detect an actual density profile associated with the elongated mass analyzed ion beam.

16. The ion implantation system ofclaim 15, wherein the plurality of Faraday cups are positioned proximate a workpiece being implanted.

17. The ion implantation system ofclaim 9, wherein the beamline system further comprises a plurality of quadrupole magnets positioned proximate the resolving aperture, the quadrupole magnets providing adjustment of a beam waist location along the path.

18. The ion implantation system ofclaim 9, wherein the beamguide further comprises a plurality of magnets providing multi-cusped magnetic fields along at least a portion of the path for beam confinement along the path within the beamguide near the resolving aperture.

19. The ion implantation system ofclaim 18, wherein the beamguide further comprises a waveguide proximate the resolving aperture and a microwave power source connected to the waveguide, the microwave power source providing microwave power to the waveguide for beam confinement along the path within the beamguide near the resolving aperture.

20. The ion implantation system ofclaim 19, wherein the microwave power and the multi-cusped magnetic fields interact within the beamguide to provide an electron-cyclotron resonance condition for beam confinement along the path within the beamguide near the resolving aperture.

21. The ion implantation system ofclaim 1, wherein the first transverse width of the elongated input ion beam and the second transverse width of the elongated mass analyzed ion beam are substantially the same.

22. A beamline system for providing an elongated mass analyzed ion beam to an end station in an ion implantation system, the beamline system comprising:

a first magnet receiving an elongated input ion beam along a path, the elongated input ion beam having a first transverse width and a first transverse height defining a first aspect ratio as a ratio of the first transverse width and the first transverse height, the first magnet providing a first magnetic field to the elongated input ion beam to direct individual ions of a desired mass along the path and to deflect ions of undesired mass away from the path; and

a second magnet located downstream of the first magnet along the path, the second magnet providing a second magnetic field to the ions of the desired mass along the path between the first magnet and the end station to direct individual ions of the desired mass to the end station in the form of an elongated mass analyzed ion beam comprising a second transverse width and a second transverse height defining a second aspect ratio as a ratio of the second transverse width and the second transverse height;

wherein the second aspect ratio is substantially the same as the first aspect ratio.

23. The beamline system ofclaim 22, comprising an entrance end and an exit end, wherein the first magnet receives the elongated input ion beam near the entrance end and the second magnet provides the elongated mass analyzed ion beam near the exit end, and wherein the first and second magnets provide the first and second magnetic fields so as to guide individual ions of the desired mass across the width of the input ion beam at the ion source to the exit end such that the individual ions of the desired mass travel generally equal distances between the entrance and exit ends.

24. The beamline system ofclaim 22, wherein the first and second magnets are substantially identical.

25. The beamline system ofclaim 22, further comprising a beamguide located along the path, the beamguide defining a beam cavity through which the elongated input ion beam travels from the entrance end to the exit end, wherein the first and second magnets provide the first and second magnetic fields across the path through first and second portions of the beamguide, respectively, to guide individual ions of a desired mass across the first transverse width of the input ion beam at the entrance end through the beam guide to the exit end such that the individual ions of a desired mass travel generally equal distances between the entrance and exit ends.

26. The beamline system ofclaim 25, further comprising a resolving aperture positioned between the first and second magnets along the path;

wherein the first magnet is positioned near the entrance end to provide the first magnetic field along the path between the entrance end and the resolving aperture so as to deflect ions from the elongated input ion beam at varying trajectories according to mass, the first magnetic field operating to direct individual ions of a desired mass through the resolving aperture along the path and to deflect ions of undesired mass away from the aperture;

wherein the resolving aperture is positioned downstream of the first magnet along the path and comprises a transverse width and a transverse height defining a resolving aperture aspect ratio different from the first and second aspect ratios; and

wherein the second magnet is positioned near the exit end of the beamguide along the path to receive ions of a desired mass traveling through the resolving aperture, the second magnet providing the second magnetic field along the path between the resolving aperture and the exit end, the second magnetic field operating to direct individual ions of the desired mass from the resolving aperture to the exit end along the path so as to provide the mass analyzed ion beam comprising the second aspect ratio.

27. The beamline system ofclaim 22, wherein the first transverse width of the elongated input ion beam and the second transverse width of the elongated mass analyzed ion beam are substantially the same.

28. A method of implanting a workpiece using an ion beam in an ion implantation system, comprising:

creating an elongated input ion beam having a first aspect ratio, the first aspect ratio being a ratio of a first transverse width and a first transverse height of the input ion beam;

mass analyzing the elongated input ion beam using a first magnetic field;

collimating the ion beam using a second magnetic field to provide an elongated mass analyzed ion beam having a second aspect ratio, the second aspect ratio being defined as a ratio of a second transverse width and a second transverse height of the mass analyzed ion beam, wherein the first and second aspect ratios are substantially the same; and

providing at least a portion of the elongated mass analyzed ion beam to at least one workpiece so as to implant the at least one workpiece with ions from the elongated mass analyzed ion beam.

29. The method ofclaim 28, wherein mass analyzing and collimating the elongated ion beam comprises providing the first and second magnetic fields to direct ions of a desired mass from an ion source to the at least one workpiece wherein individual ions of the desired mass travel generally equal distances between the ion source and the at least one workpiece.

30. An ion implantation system for implanting a workpiece using an ion beam, comprising:

means for creating an elongated input ion beam having a first aspect ratio the first aspect ratio being a ratio of a first transverse width and a first transverse height of the input ion beam;

means for mass analyzing the elongated input ion beam using a first magnetic field;

means for collimating the ion beam using a second magnetic field to provide an elongated mass analyzed ion beam having a second aspect ratio substantially the same as the first aspect ratio, the second aspect ratio being defined as a ratio of a second transverse width and a second transverse height of the mass analyzed ion beam; and

means for providing at least a portion of the elongated mass analyzed ion beam to at least one workpiece so as to implant the at least one workpiece with ions from the elongated mass analyzed ion beam.

31. The system ofclaim 30, wherein the means for mass analyzing the elongated input ion beam comprises a first magnet, and wherein the means for collimating the ion beam comprises a second magnet substantially identical to the first magnet.

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